Work is progressing on a major project to restore the famous Nyboder houses in Copenhagen. These long terraced rows, with cobbled streets and narrow yards between the rows, cover a large block in the north-east part of the historic centre of the city within the old city defences … so south and west of Kastellet - the fortress or citadel - and close to Østerport railway station that is on the site of the old east gate.

The first of the rows were built in the 1630s and 1640s at the instigation of Christian IV for naval personnel and were single storey but with attic rooms. More rows - the two-storey terraces - were constructed in the middle of the 18th century and the last houses, in grey brick, date from the very end of the 19th century.

The houses from the 17th and 18th centuries were built in pale-yellow brick but given an external wash of lime with deep ochre pigment but this wash has just been removed so the brickwork can be repaired and, where necessary, repointed.

Stripped of this ochre wash, the facades reveal important archaeological evidence to show clearly how window and door openings were constructed. There were no obvious lintels but lines of headers above the windows so, almost certainly, the timber frame of the floor structure would have been set out to take the weight and outward thrust of the roof to prevent the outer walls bowing out or the ground-floor openings failing under the weight of the brickwork and roof above.

In contrast, more precise coursing in historic brickwork can be seen in a house on Wilders Plads in Christianshavn with alternate rows of different colours of brick so that brickwork was clearly built to be exposed and left without render. The Nyboder brickwork is not of the same quality so the houses must have been covered and protected with was of lime and pigment from the start.

It is also clear that by using lime wash - rather than a thicker and smooth coat of render - the final surface is not just more resilient - as each thin layer is applied, the lime oxidises and bonds to the stone or brick it covers - but the visible and slightly irregular brickwork gives a texture to the surface that seems to make the colour deeper … modern brickwork, in contrast, seems mechanical and flat or, if anything, dull.